Pressure measuring devices are used for the measurement of pressures—especially, absolute pressures, relative pressures, and differential pressures—and are used in industrial measurement technology.
In pressure measurement technology, so-called semiconductor pressure sensors are frequently used. Semiconductor sensors are today regularly produced that are based upon silicon, e.g., using silicon-on-insulator (SOI) technology. They are fashioned, for example, as pressure sensor chips that typically have a membrane carrier and a measurement membrane arranged on the membrane carrier.
These pressure sensors are very sensitive and are therefore placed in a housing that as a rule is metallic, and are subjected to the pressure to be measured via a diaphragm seal that is connected upstream and that is filled with a liquid that transmits pressure. The housing and the pressure sensor are thus made of different materials that have very different coefficients of thermal expansion. Therefore, as a result of the mechanical connection between the housing and the pressure sensor required for the sensor assembly, mechanical stresses can occur that affect the transmission characteristic of the measurement membrane, thus impairing the achievable measurement precision and its reproducibility. This holds especially for a temperature-dependent hysteresis of the measurement results.
In order to reduce temperature-dependent stresses acting on the pressure sensor, German Patent, DE 10 2007 052 364 A1 describes the arrangement of the pressure sensor chip on a ceramic intermediate carrier that has a coefficient of thermal expansion that matches the coefficient of thermal expansion of the semiconductor material. The intermediate carrier is glued directly onto a metallic carrier of the housing via an adhesive bond realized with an elastic adhesive. Kovar is indicated as the material for the carrier. Kovar has a coefficient of thermal expansion of 6 ppm/K, and is therefore significantly closer to the coefficient of thermal expansion of silicon—used for pressure sensors—of 2.6 ppm/K than more standard housing materials, which are also significantly lower in cost, such as stainless steel, which has a coefficient of thermal expansion of 16 ppm/K.
In the described pressure measurement devices, the ceramic intermediate carrier has a base surface that is larger than the base surface of the pressure sensor arranged thereon. This has the consequence that, despite the comparatively well-matched coefficient of thermal expansion of the intermediate layer, remaining thermal mechanical stresses can have effects on the pressure sensor over the entire base surface.
As an alternative to this, complementary solution approaches are known from the prior art, in which a reduction in temperature-dependent stresses acting on the pressure sensor is achieved by arranging the pressure sensor on a base whose base surface is significantly smaller than the base surface of the pressure sensor mounted thereon. For this purpose, two different specific embodiments are known, which are described, for example, in German Patent, DE 34 36 440 A1. In one specific embodiment, the base is an integral component of the metallic carrier of the housing, and is made of the material of the housing. In the second specific embodiment, the base is fashioned as a separate component that is placed into a bore in the carrier by means of a glazing. The glazing offers the advantage that it brings about an electrical insulation of the pressure sensor against the housing. However, the material combinations of the base material and the carrier material, between which hermetically-sealed glazings can be produced, are limited.